On 2014-12-04 08:53, Shriramana Sharma wrote:
> I observe that whenever I create a BtrFS instance using mkfs.btrfs,
> there is always the leftover cruft of two System/Metadata-Single
> allocation profiles:
>
> btrfs fi df /run/media/samjnaa/BRIHATII/
> Data, single: total=460.01GiB, used=458.47GiB
> System, DUP: total=8.00MiB, used=80.00KiB
> System, single: total=4.00MiB, used=0.00B
> Metadata, DUP: total=1.50GiB, used=736.86MiB
> Metadata, single: total=8.00MiB, used=0.00B
> GlobalReserve, single: total=256.00MiB, used=0.00B
>
> Doing btrfs balance eventually removes these (but since I forgot to do
> it *before* copying 400+ G of data to the drive it's still running)
> but I don't understand why these have to be created in the first
> place? (I just used SuSE Tumbleweed's default mkfs.btrfs without any
> -m or -d options.)
>
SuSE may have an old version of btrfs-progs then (which wouldn't 
surprise me, it is an 'enterprise' distribution after all), because I 
haven't seen this on anything since 3.16.

The really interesting thing in this case is that the metadata chunk is 
8M, when they are usually 256M.

Also, for future reference, you can use the switch -mprofiles=single to 
just balance out those chunks.